Blue print and process of making the same



y 31, 1932- H. J. BRUNK 1,861,298

BLUE PRINT AND PROCESS OF MAKING THE SAME Filed May 11. 1931 Patented May 31, 1932 UNITED STATES PATENT OFFICE HAROLD J. BRUNK, OF CHICAGO, ILLINOIS, ASSIGNOR TO THE C. F. PEASE COMPANY, A.

CORPORATION OF- DELAWARE BLUE PRINT AND PROCESS OF MAKIIVG THE SAME- Application filed May 11, 1931. Serial No. 536,378.

' is developed, resulting in a. blue sheet with white'lines on it, or a white sheet with blue lines on it.

I The coating is applied as a solution containing mixtures of potassium ferricyanide and organic salts of iron such as ferric ammonium oxalate. During the period of exposure to such light the potassium ferricyanide is partly reduced to potassium ferrocyanide while the ferric ammonium oxalate is reduced to ferrous ammonium oxalate.

After exposure, the paper is washed with clear water which removes all the unexposedchemical from the areas which were behind the opaque portion of the tracing or negative and also removes the loose exposed or reduced chemical, i. e., that portion which does not adhere to the fibres of the paper. This washing, in a certain sense, also starts the process of oxidation of the reduced chemical which action is necessary in the formation of the blue lines or areas. In other words, if left long enough in the water the so-called potash treatment hereinafter referred to, is unnecessary. It is the practice, however, to complete the oxidation by applying bichromate of potash or some other strong oxidizing agent to the surface of the paper immediately after the applicatlon of the first Water wash. The. excess bichromate or potash must be washed off the surface by applying a second water wash, after which the paper is ready for drying.

Prints made in this manner are far from satisfactory or dependable when first class blueprints with clear white lines or blue line When making blue line prints or blue lines on a white background from negatives of tracings, the fully exposed chemical in the area outside of or between negatives runs down into the white background and stains it blue immediately when Water is applied to the surface of the paper.

The blue lines themselves at certain exposures run down into the white ground givin them a ragged appearance.

n the case .of blue prints, or white lines on a blue ground (which are obtained when a tracing or positive original is used) the blue in the ground runs over the line giving it a bluish cast and at the same time closing up on the line making it narrower than the line on the original tracing and at full exposures of the blue ground the line may be lost completely.

Due to the fact that this running of the blue takes place at or near the point of full exposure or reduction by light it is customary to make prints under-exposed with the idea of eliminating this burning out of the white lines as it is commonly called. In making prints under-exposed or only partially reduced the deep Prussian blue color desired is never obtained; therefore, seldom,

if ever, is the chemical on the paper changed to the color it is capable of producing.

In trying to avoid this undesirable running at the sacrifice of color, the operator is forced to operate the printing machine within very close limits of speed or exposure time, which fact necessitates the preparation of sensitized paper of several printing speeds when covering the range of average printingwhich is from six inches to twelve feet per minute.

Various methods of washing have been tried with the idea of preventing this running or bleeding mentioned above but none has proven' successful heretofore. No method of changing the application of water is successful because the bleeding is caused by the formation of insoluble Prussian blue when the unexposed chemical on the print mixes with or combines with the exposed or reduced portions. The Prussian blue formed, runs into the white and cannot be washed out, once it stains the print. From this it is evident that moisture applied to the paper in a quantity sufiicient to remove the surplus chemical, regardless of how applied, is bound to cause the exposed chemical to mix with the unexposed portion, as nothing separates the two, and even if the blue formed is not in suflicient quantities to run very far, the line itself will be unsatisfactory.

The general object of the present invention is to overcome the foregoing difiiculties by an improved process of developing the prints resulting in the elimination of bleeding. regardless of the speed of operation of the blueprint machine or of the length of exposure, and which also results in the production of clear white full lines on blueprints, a perfectly white background on blue line prints, a deep Prussian blue following full exposures and one which does not fade readily, a wide range of exposure without the need of many different printing speeds and the successful printing from tracings or from negatives without changing the speed.

A contributory object is to attain the foregi-ng advantages by developing the paper immediately after printing and before any water has been applied to the surface. after which the prints are washed and may then be treated with an oxidizing agent.

Otherwise expressed. the present invention is directed to sensitizing paper with ferri compounds. exposing the sensitized paper to a source of light with portions of the surface shielded from the source of light whereby the compounds of the exposed portion of the sensitized paper are reduced to a ferrous state. Thereafter, the paper is treated with adeveloper containing ferric compounds adapted to render insoluble the reduced ferrous compounds and the so treated paper is then washed with water. Preferably the ferri compounds of the developer are of the same chemical characteristics as the ferri compounds used to sensitize the paper.

More specifically. paper or other suitable material, is sensitized with a ferricyanide and after exposure a reducing agent is used to convert the ferricyanide to ferrocyanide. The reducing agent at the same time is capable of forming with the reduced ferrocyanide a blue precipitate (Prussian blue) having high tinctorial value. Any diffusion of the reduced ferrocyanide into the unexposed portions, such as would-result in the formation of the same precipitate 'in the unexposed portions as is produced in the exposed portions, is prevented by fixing, i'. e., precipitating said reduced ferrocyanide prior to washing with water.

A practical sensitizing formula is as follows: Potassium ferricyanide, 5 pounds in 5 gallons of water. Ferric ammonium oxalate, 34 pounds in 12 gallons of water. Ammonium oxalate, 1 pounds in 4 gallons of Water. Mix above together making a total batch of 21 gallons of solution.

An appropriate developer for the above would be: 1 pound potassium ferricyanice in 1 gallon of water. 5 pounds ferric ammonium oxalate in 2 gallons of water. Mixing together gives 3 gallons of developer.

In the accompanying drawing I have illustrated a machine designed for carrying out the improved process.

Fig. 1 is a side elevation thereof;

Fig. 2 is an elevation of the opposite end of the developing attachment.

The frame of the machine 10 is similar to that of a well-known type of printing, washing and drying machine now on the market and since much of the mechanism is used in said commercial machine, except for the means for applying the developingsolution between the printing stage and the water washing stage, said machine will be described very briefly.

The sensitized paper is supported on a suitable roller 11, at one end of the machine, the paper 12 being drawn past a sheet of curved glass 13, where it is exposed to. a suitable source of light (preferably a row of arc lights) in a well-known manner, the paper leaving the printing section of the machine where it passes over a roller 14 and then under a roller 15, the weight of which is supported in part by the loop of paper as shown, thereby maintaining the proper tension on the paper and providing for expansion and contraction of the same.

The paper then passes the means for applying the developer which may have the form of a roll 16 dipping in a pan 17 containing a developing solution supplied by a suitable reservoir 18.

This roll, pan and associated parts may be in the form of an attachment, readily applicable to existing machines.

From the developer the paper travels past the first water wash consisting of atube 19 with suitable nozzles which direct sprays of water against the inclined surface of the paper in a manner which has been used heretofore. the paper thereafter travelling over suitable rollers to the potash roller 20 which dips in a pan 21, supplied with bichvomate of pot-ash or other suitable oxidizing agent, contained in a reservoir 22. The paper then travels upwardly past the final water Wash, the Water being supplied from the pipe 23, and thereafter passes through the dryer 24, where it is dried in the usual manner, and thereafter wound on a removable roller 25.

The chemical mechanism of the process may be more fully appreciated by reference to the following diagrammatic scheme representing the composition of the chemicals on the paper in the unreduced (unexposed) and reduced (exposed) portions respectively:

X Unreduced Reduced K Ferric (Fe+++) radical or ion Ferrous (Fe++) radical or ion X represents the dividing line between the exposed and unexposed portions of the sensitized paper and it is an object of this invention to have this line sharply defined and prevent encroachment of the chemicals in the reduced area upon those of the unreduced area and vice versa. y

In this diagram only the more essential portions, i. e., ions or radicals of the reacting substances have been shown. For example, potassium, sodium or other soluble ferricyanide may be used, the ferricyanide being the important consideration. This will be readily understood by those familiar with the ionic theory or doctrine concerning which reference may be had to standard treatises on physical chemistry, e. g. Physical Chemistry for Colleges by Millard and Tlheoretical Chemistry by Noyes and Sherr1 The photochemical reaction consists in the reduction of ferricyanide to ferrocvanide by the conjoint action of sunlight and a photo sensitive reducing agent, as for example, an organic ferric salt broadly and. more specifically. ferric ammonium oxalate. There is no useful reaction between a ferric salt and a ferricyanide but a ferric salt and a ferrocyanide react to produce a deep blue highly tinctorial water insoluble substance. In the old process the ferricyanide was reduced to ferrocyanide and the ferric salt to ferrous salt in the exposed portions. and upon treatment-with wash water a migration over the line X took place, as shown by the arrows in the above diagram. resulting in an impairment or destruction of. the high- 1y desirable sharp definition between the exposed and unexposed portions.

The foregoing procedure prevents the combination on paper of 1) the ferrous ammonium oxalate and potassium ferricyanide that was not exposed to the light, in the course of printing, and the potassium ferrocyanide With any ferric ammonium oxalate that was not exposed to light in the course of printing. After developing as above, the prints are washed in a clear water Wash and then completely oxidized with bichromate of potash or other agent, as previously stated, and the surplus can then be washed off and the prints ready for drying.

The broad teaching tion is that such migration or diffusion is prevented by fixing the reduced ferrocyanide before washing the paper. By this fixing process the ferrocyanide is rendered insoluble and incapable of reacting with the ferric salt in the unreduced portions. This fixing is carriedout, as explained, by washing the paper with a solution of a ferric salt, containing ferric Fe ions, which reacts with the errocyanide in the exposed portions and converts it to insoluble ferric ferrocyanide. In those cases where a ferric organic salt is employed as the photosensitive reducing agent and is itself reduced to the ferrous condition, the fixing solution should also contain an agent, as for example a ferricyanide, to fix the ferrous salt and pre vent it from difiusing and combining with ferricyanide in the unexposed portions.

Testshave been made with a large number of possible developers including all of the common ferric compounds and most of the rare and other metallic salts, from which the following show possibilities as developers:

Potassium ferricyanide.

I Ferric ammonium oxalate.

Ferric-ammonium citrate.

Ferric-sodium oxalate.

Ferric chloride.

Ferric potassium oxalate.

Sodium perborate.

The potassium ferricyanide and the ferric ammonium oxalate in combination are by far the best and the potassium ferricyanide works well alone on the slower printing papers. The relative amount of potassium ferricyanide and ferric ammonium oxalate can be changed to give different shades of blue, the deeper shades of blue being obtained when the relative amounts of potassium ferricyanide in the sensitizing formula and in the developing solution balance. For example, a fast printing paper has less potassium ferricyanide in the formula than a slow printing paper; therefore, less should be used in the developing solution.

In addition to potassium bichromate other oxidizing agents may be used, such as other bichromates, hydrogen dioxide, sodium prbora-te, potassium persulphate, and potassium ferricyanide. It is understood that the use of any of these agents follows the washing of the paper. Most of those listed as alternatives are too slow in their action for commercial use. For many purposes it is sufiicient to wash the print and apply no further chemical treatment. In other words, the oxidation is not necessary, particularly if the machine is run slowly to give full reduction, in which case the bichromate of potash or equivalent may be omitted, although its use adds somewhat to the color.

of the present inven- The resulting prints constitute a remarkable improvement over blueprints and socalled white prints, and the like, made by the prevailing method, in that there is no running or bleeding of the blue line into the white areas at any speed or exposure, the blueprints show clear white full lines on a deep Prussian blue background, the blue line prints show a perfectly white background, the deep blue color fades slower than the present shades of blue when exposed to sunlight, and there is a wide range of exposure permissible which eliminates the need of providing sensitized papers with various different printing speeds.

It has been proposed heretofore to develop the unexposed portions of prints, i. e. the parts which were temporarily under the lines, which shielded them from the light. In the present invention, the exposed reduced portions of the prints are developed.

What I claim is:

1. The method of making non-bleeding photoprints comprising coating a sheet of material with a ferricyanide of an alkali metal and a light sensitive ferric ammonium compound of an organic acid, exposing portions of the coated surface to light, applying to said surface without preliminary watering a developer comprising a ferricyanide of an alkali metal and a ferric ammonium compound of an organic acid, and thereafter washing.

2. The method of making non-bleeding photoprints comprising coating a sheet of material with a ferricyanide of an alkali metal and a light sensitive ferric ammonium compound of a carboxylic acid, exposing portions of the coated surface to light, applying to said surface without preliminary waterlng a developer comprisin a ferricyanide of an alkali metal and a erric ammonium compound of a carboxylic acid, and thereafter washing.

3. The method of making non-bleeding photoprints comprising coating a sheet of material with potassium ferricyanide and ferric ammonium oxalate, exposing portions of the coated surface to light, applying to said surface without preliminary watering a developer comprising potassium ferricyanide and ferric ammonium oxalate, and thereafter washing.

4. The method of making non-bleeding photoprints comprising coating a sheet of material with potassium ferricyanide and an additional organic salt of iron, exposing portions of the coated surface to light, applying to said surface a solution of ferric ammonium oxalate, potassium ferricyanide and water, the volume of the ferric ammonium oxalate exceeding the combined volumes of the other two ingredients.

5. The method of making non-bleeding photoprints comprising coating a sheet of material with potassium ferricyanide and ferric ammonium oxalate, exposin portions of the coated surface to light, applying to said surface adeveloping solution and thereafter washing, said developing solution comprising 1 pound potassium ferricyanide in 1 gallon of water and 5 pounds ferric ammonium oxalate in 2 gallons of water.

6. The method of producing non-bleeding photoprints comprising sensitizing paper with a coating of a soluble ferricyanide and a soluble ferric compound, exposing a portion of the sensitized surface to actinic rays to reduce the trivalent iron ions of the exposed portion of the coating to divalent iron ions, treating the sensitized surface with an iron containing developer having present a ferricyanide and a ferric compound dissociating into trivalent iron ions, the latter reacting simultaneously with substantially all of the divalent iron ions to produce water insoluble iron compounds and thereby prevent bleeding on subsequent washing, and thereafter washing said paper to remove the soluble salts and obtain sharp definition between the exposed gnd unexposed portion of the sensitized surace.

7. The method of producing non-bleeding photoprints comprising sensitizing paper with a coating of a soluble ferricyanide and a soluble ferric organic compound, exposing a portion of the sensitized surface to actinic rays to reduce the trivalent iron ions of the exposed portion of the coating to divalent iron ions, treating the sensitized surface with an iron containing developer containing a ferricyanide and a ferric compound dissociating into trivalent iron ions adapted to simultaneously react with substantially all of the divalent iron ions and form water insoluble iron compounds acting to prevent bleeding on subsequent washing, and thereafter washing said paper to remove the soluble salts and obtain sharp definitions between the exposed efind unexposed portions of the sensitized surace.

8. The method of producing non-bleeding photoprints comprising sensitizing paper with a coating of a soluble ferricyanide and a soluble ferric organic compound, exposing a portion of the sensitized surface to actinic rays to reduce the trivalent iron ions of the exposed portion of the coating to divalent iron ions, treating the sensitized surface with an iron containing developer having present a ferricyanide and an inorganic ferric compound dissociating into trivalent iron ions adapted to simultaneously react with substantially all of the divalent iron ions to form water insoluble iron compounds acting to prevent bleeding on subsequent washing, and thereafter washing said paper to remove the soluble salts and obtain sharp definition between the exposed and unexposed portions of the sensitized surface.

9. The method of producing non-bleeding photoprints comprising sensitizing paper with a coating of a soluble ferricyanide and a soluble ferric compound, exposing a portion of the sensitized surface to actinic rays to reducethe trivalent iron ions of the exposed portion of the coating to divalent iron ions, treating the sensitized surface with an iron containing developer having present a ferricyanide and a ferric compound dissociating into trivalent iron ions, the latter reacting simultaneously with substantially all of the divalent irons ions to form a mixture of Turnbulls blue and Prussian blue and thereby preventing bleeding on subsequent washing, and thereafter washing said paper to remove the Water insoluble salts and obtain sharp definition between the exposed and unexposed portions of the sensitized surface.

In testimony whereof, I have subscribed my name.

HAROLD J. BRUNK. 

